Catalytic reforming is a well-established industrial process in the refining industry for improving the octane quality of naphtha and in petrochemical industry for the production of aromatics. In catalytic reforming, a bi-functional catalyst (having metal function and acidic function) is employed, which governs reactions such as dehydrogenation and hydrogenation of naphthenes. The conventional catalyst used for catalytic naphtha reforming process is platinum (Pt) alone or in combination with rhenium (Re), iridium (Ir), tin (Sn) or germanium (Ge) promoted on a gamma alumina support. The gamma alumina support usually contains chloride to provide the acid function to the catalyst which governs reactions, such as dehydrocyclization, hydrocracking, isomerization, and the like.
However, the catalyst gets deactivated during the afore-stated reactions, mainly due to coking. As the coke builds up on the catalyst surface, the reaction temperature has to be increased gradually to offset the loss of catalyst activity. Over a period of time it becomes economically infeasible to continue the operations and thus, the catalyst requires to be regenerated. Based on the frequency of regeneration of the catalyst, processes are broadly classified as (1) Semi-regenerative or (2) Continuous Catalytic Regenerative (CCR) type.
Fixed-bed reactors are usually employed in semi-regenerative process. In the semi-regenerative process, the reformer unit is taken off the stream and the total catalyst in the unit is regenerated. The activity levels of a regenerated catalyst is close to that of a fresh catalyst obtained at the start of a′ successive cycle of operation. Commercially, the preferred catalyst used in semi-regenerative unit is Pt—Re/Al2O3 which is found to be stable.
In a continuous reforming process, moving-bed reactors are used, where the catalyst is moved continuously through the reactors and is withdrawn from the last reactor for regeneration in a regeneration section and returned to the first reactor as virgin catalyst. Thus, there is no production loss due to down time and catalyst deactivation. The CCR reformer can be operated continuously under severe conditions. The other major advantages of this operation are high catalyst activity and selectivity. The catalyst formulation Pt—Sn/Al2O3 offers high selectivity at low pressure and thus is a good choice in continuous reforming units. The other advantages of Pt—Sn/Al2O3 include increased activity and selectivity to aromatic formation through higher paraffin dehydrocyclization, decreased rate of deactivation compared to platinum-only catalysts, ability to attain a high degree of platinum dispersion, and resistance to agglomeration.
In a reforming catalyst a certain level of catalyst acidity is required to initiate essential isomerization reactions; however, the presence of increased acidity due to chlorination, leads to yield loss and catalyst deactivation. A requirement in catalytic reforming is to improve selectivity to liquid products and yield of aromatics by reducing the formation of light C1-C4 gaseous products which are produced by acid cracking reactions.
Although, commercially successful catalysts have been developed, there still exists a need for further improvement, especially with regard to catalyst activity, selectivity and stable performance. Also, there is a need for improving the reformate yield and simultaneous suppression of acid site cracking.